1. Field of the Invention
The present invention relates to a liquid crystal display (LCD) device, and more particularly to a liquid crystal display device using a light-cured sealant.
2. Description of the Related Art
First, a conventional liquid crystal display device 100 will be described with reference to FIGS. 1a and 1b. FIG. 1a is a perspective view of the conventional liquid crystal display device, and FIG. 1b is a sectional view taken along line 1b—1b of FIG. 1a. Referring to FIG. 1b, the conventional liquid crystal display device 100 includes a first substrate 102 (i.e., a color filter substrate) and a second substrate 104 (i.e., a thin film transistor substrate) disposed to face each other with a predetermined gap therebetween. A liquid crystal layer 106 is sandwiched between the substrates 102 and 104. The substrates 102 and 104 are affixed to each other by a sealant 107.
Referring to FIG. 1a, the thin film transistor substrate 104 includes: a plurality of parallel data lines 108 and a plurality of parallel gate lines 110 which are formed on the surface of a glass substrate 112 facing the liquid crystal layer 106; and thin film transistors (TFTs) 114 disposed at each of the intersections of the data lines 108 and the gate line 110. Each region defined by two adjacent data lines 108 and two adjacent gate lines 110 is provided with a pixel electrode 116 connected to the drain electrode of the corresponding TFT 114.
Referring to FIG. 1b, the color filter substrate 102 includes: a plurality of colored portions 118 on the surface thereof facing the liquid crystal layer 106 at positions corresponding to the pixel electrodes 116 of the thin film transistor substrate 104; and a counter electrode 120 formed over the colored portions 118. A light-shielding matrix (like black matrix) 122 is disposed between the adjacent colored portions 118.
The light-shielding matrix 122 is made of a light-blocking material or a light-absorbing material for absorbing external light and improving the contrast of a displayed image. As shown in FIG. 1b, the light-shielding matrix 122 disposed in the periphery of the liquid crystal display device 100 covers a portion of the sealant 107 such that light can't penetrate through it to reach the portion of the sealant.
Therefore, when a UV curable sealant is used to seal the liquid crystal display device 100, since a portion of the sealant 107 is (especially the interface between the liquid crystal layer 106 and the sealant 107) covered by the light-shielding matrix 122, the UV light is unable to reach the covered portion of the sealant 107 thereby resulting in incomplete curing thereof. Therefore, that uncured sealant will react with the liquid crystal layer and cause the latter to degrade in its performance as a liquid crystal material.
In the field of flat panel display, the two substrates may be affixed to each other with a thermosetting sealant. However, this method needs a relatively high curing temperature which the liquid crystal cannot tolerate, and therefore the step of curing the thermosetting sealant should be conducted prior to filling of the liquid crystal material.
However, in a newly proposed technique based on a one drop fill (abbreviated ODF) method disclosed in U.S. Pat. No. 5,263,888 to Ishihara et al., one of the substrates receives droplets of liquid crystal material prior to joining it with the other substrate. This greatly reduces the number of the manufacturing steps and increases the manufacturing efficiency. However, since the liquid crystal material is dropped prior to the step of sealing the two substrates, this method cannot use the thermal setting sealant but must use the UV curable sealant instead.
Therefore, in order to ensure that the UV curable sealant can be cured completely thereby preventing it from reacting with the liquid crystal material, the light-shielding matrix that blocks the sealant from light must be kept away from the sealant. But this means the redundant area outside the display region of liquid crystal panel will increase or the area of the display region will decrease if the area of the liquid crystal panel remains the same, either the former design or the latter design varies from the developing trend of the liquid crystal display device.
The present invention therefore seeks to provide a liquid crystal display device that overcomes or at least reduces the above-mentioned problems of the prior art.